"There is a natural warm water aquifer that is creating a pocket of warmer water in the pond, which is where a lot of the bait fish and barra are congregating, but the fish are under stress," Mr Dowling told AAP on Thursday.

The fisheries executive says the fish are swimming close to the surface looking for food or warmer water, which was not normal behaviour.

"The next six weeks are critical for us so we will be monitoring the fishery weekly to see how the fish are going," Mr Dowling said.